Plasma treatment method and apparatus

ABSTRACT

A plasma treatment method comprising exhausting a process chamber so as to decompress the process chamber, mounting a wafer on a suscepter, supplying a process gas to the wafer through a shower electrode, applying high frequency power, which has a first frequency f 1  lower than an inherent lower ion transit frequencies of the process gas, to the suscepter, and applying high frequency power, which has a second frequency f 2  higher than an inherent upper ion transit frequencies of the process gas, whereby a plasma is generated in the process chamber and activated species influence the wafer.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a plasma treatment method bywhich substrates such as semiconductor wafers are etched or sputteredunder plasma atmosphere. It also relates to a plasma treatment apparatusfor the same.

[0003] 2. Description of the Related Art

[0004] Recently, semiconductor devices are more and more highlyintegrated and the plasma treatment is therefore asked to have a finerworkability in their making course. In order to achieve such a finerworkability, the process chamber must be decompressed to a greaterextent, plasma density must be kept higher and the treatment must have ahigher selectivity. In the case of the conventional plasma treatmentmethods, however, high frequency voltage becomes higher as output ismade larger, and ion energy, therefore, becomes stronger than needed.The semiconductor wafer becomes susceptible to damage, accordingly.Further, the process chamber is kept about 250 mTorr in the case of theconventional methods and when the degree of vacuum in the processchamber is made higher (or the internal pressure in the chamber is madesmaller), plasma cannot be kept stable and its density cannot be madehigh.

SUMMARY OF THE INVENTION

[0005] When gases are made plasma, the action of ions in the plasmabecomes different, depending upon frequencies of high frequency power.In short, ion energy and plasma density can be controlled independentlyof the other when high frequency power having two different frequenciesis applied to process gases. However, ions (loaded particles) easily runfrom plasma to the wafer at a frequency band, but it becomes difficultfor them to run from the plasma sheath to the wafer at another frequencyband (or transit frequency zone). The so-called follow-up of ionsbecomes unstable.

[0006] Particularly molecular gases change their dissociation, dependingupon various conditions (such as kinds of gas, flow rate, high frequencypower applying conditions and internal pressure and temperature in theprocess chamber), and the follow-up of ions in the plasma sheath changesin response to this changing dissociation. Further, the follow-up ofions at the transit frequency zone also depends upon their volume (ormass). Particularly in the case of molecular gases used in etching andCVD, the dissociation of gas molecules progresses to an extent greaterthan needed when electron temperature becomes high with a littleincrease of high frequency power, and the behavior of ions in the plasmasheath changes accordingly. Plasma properties such as ion currentdensity become thus unstable and the plasma treatment becomes uneven,thereby causing the productivity to be lowered.

[0007] When the frequency of high frequency power is only made high toincrease plasma density, the dissociation of gas molecules progresses tothe extent greater than needed. It is therefore desirable that theplasma density is raised not to depend upon whether the frequency ishigh or low.

[0008] An object of the present invention is therefore to provide plasmatreatment method and apparatus capable of controlling both of thedissociation of gas molecules and the follow-up of ions and also capableof promoting the incidence of ions onto a substrate to be treated.

[0009] Another object of the present invention is to provide plasmatreatment method and apparatus capable of raising the plasma densitywith smaller high frequency power not to damage the substrate to betreated. According to the present invention, there can be provided aplasma treatment method of plasma-treating a substrate to be treatedunder decompressed atmosphere comprising exhausting a process chamber;mounting the substrate on a lower electrode; supplying plasma generatinggas to the substrate on the lower electrode through an upper electrode;applying high frequency power having a first frequency f₁, lower thanthe lower limit of ion transit frequencies characteristic of processgas, to the lower electrode; and applying high frequency power having asecond frequency, higher than the upper limit of ion transit frequenciescharacteristic of process gas, to the upper electrode, whereby a plasmagenerates in the process chamber and activated species influence thesubstrate to be treated. it is preferable that the first frequency f₁ isset lower than 5 MHz, more preferably in a range of 100 kHz-1 MHz. It isalso preferable that the second frequency f₂ is set higher than 10 MHz,more preferably in a range of 10 MHz-100 MHz.

[0010] High frequency power having the frequency lower than the lowerlit of ion transit frequencies is applied to the lower electrode.Therefore, the follow-up of ions becomes more excellent and ions can bemore efficiently accelerated with a smaller power. In addition, both ofion and electron currents change more smoothly. Further, the follow-upof ions does not depend upon kinds of ion. The plasma treatment can bethus made more stable even when the degree in the process chamber andthe rate of gases mixed change. On the other hand, high frequency powerhaving the frequency higher than the upper limit of ion transitfrequencies is applied to the upper electrode. Therefore, ions can beleft free from frequencies of their transit frequency zone to therebyenable more stable plasma to be generated.

[0011] Ion transit frequency zones of process gases used by the plasmatreatment in the process, such as s etching, CVD and sputtering, ofmaking semiconductor devices are almost all in the range of 1 MHz-10MHz.

[0012] Impedances including such capacitive components that theimpedance relative to high frequency power becomes smaller than severalkΩ and that the impedance relative to relatively low frequency powerbecomes larger than several a are arranged in series between the upperelectrode and its matching circuit and between them and the ground.Current is thus made easier to flow to raise the plasma density and ioncontrol.

[0013] Additional objects and advantages of the invention will be setforth in the description which follows, and in part will be obvious fromthe description, or may be learned by practice of the invention. Theobjects and advantages of the invention may be realized and obtained bymeans of the instrumentalities and combinations particularly pointed outin the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The accompanying drawings, which are incorporated in andconstitute a part of the specification, illustrate presently preferredembodiments of the invention and, together with the general descriptiongiven above and the detailed description of the preferred embodimentsgiven below, serve to explain the principles of the invention.

[0015]FIG. 1 is a block diagram showing the plasma etching apparatusaccording to an embodiment of the present invention;

[0016]FIG. 2 is a flow chart showing the plasma etching method accordingto an embodiment of the present invention;

[0017]FIG. 3 shows a waveform of frequency applied to an upper (orsecond) electrode;

[0018]FIG. 4 shows a waveform of frequency applied to a lower (or first)electrode (or suscepter);

[0019]FIG. 5 is a graph showing transit frequency zones of variousgases;

[0020]FIG. 6 is a block diagram showing the plasma etching apparatusaccording to another embodiment of the present invention;

[0021]FIG. 7 is a block diagram showing the plasma etching apparatusaccording to a further embodiment of the present invention;

[0022]FIG. 8 is a block diagram showing the plasma etching apparatusaccording to a still further embodiment of the present invention;

[0023]FIG. 9 is a vertically-sectioned view showing a housing and a ringmember of the plasma etching apparatus;

[0024]FIG. 10 is a vertically-sectioned view showing the ring memberbeing cleaned;

[0025]FIG. 11 is a vertically-sectioned view showing the ring memberbeing cleaned;

[0026]FIG. 12 is a perspective view showing an upper shower electrodeand a semiconductor wafer dismantled;

[0027]FIG. 13 is a block diagram showing the plasma etching apparatusaccording to a still further embodiment of the present invention;

[0028]FIG. 14 is a vertically-sectioned view showing the plasma etchingapparatus when the suscepter is lowered;

[0029]FIG. 15 is a vertically-sectioned view showing the plasma etchingapparatus when the suscepter is lifted;

[0030]FIG. 16 is a partly-sectioned view showing a wafer carry-in and-out gate and a baffle member;

[0031]FIG. 17 is a partly-sectioned view showing the wafer carry-in and-out gate and another baffle member;

[0032]FIG. 18 is a block diagram showing the plasma etching apparatusaccording to a still further embodiment of the present invention;

[0033]FIG. 19 is a perspective view showing a cover for the upper showerelectrode;

[0034]FIG. 20 is a perspective view showing another cover for the uppershower electrode;

[0035]FIG. 21 is a vertically-sectioned view showing the cover for theupper shower electrode;

[0036]FIG. 22 is a plan view showing the cover for the upper showerelectrode;

[0037]FIG. 23 shows how the cover is attached to the upper showerelectrode;

[0038]FIG. 24 shows how the cover is detached from the upper showerelectrode;

[0039]FIG. 25 is a sectional view showing the cover being cleaned;

[0040]FIG. 26 is a sectional view showing a further cover;

[0041]FIG. 27 is a sectional view showing a still further cover;

[0042]FIG. 28 is a sectional view showing a still further cover;

[0043]FIG. 29 is a block diagram showing a magnetron plasma etchingapparatus in which plasma is being generated;

[0044]FIG. 30 is a perspective view showing a baffle member arranged onthe side of the suscepter;

[0045]FIG. 31 is a vertically-sectioned view showing a hole formed inthe baffle member;

[0046]FIG. 32 is a vertically-sectioned view showing another hole formedin the another baffle member;

[0047]FIG. 33 shows plasma generated in the conventional apparatus;

[0048]FIG. 34 is in tended to explain the relation of the processchamber to magnetic field generated by a permanent magnet;

[0049]FIG. 35 is a block diagram showing the plasma etching apparatusaccording to a still further embodiment of the present invention;

[0050]FIG. 36 is a block diagram showing the inside of a vaporizer;

[0051]FIG. 37 is a sectional view showing another vaporizer;

[0052]FIG. 38 is a sectional view showing a further vaporizer;

[0053]FIG. 39 is a perspective view showing a still further vaporizer;

[0054]FIG. 40 is a sectional view showing a pipe in which plural kindsof gas axe mixed;

[0055]FIG. 41 is a block diagram showing a plasma CVD apparatus providedwith the vaporizer;

[0056]FIG. 42 is a sectional view showing the inside of the conventionalvaporizer; and

[0057]FIG. 43 is a graph showing the change of gas flow rate at theinitial stage of gas supply.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0058] Some embodiments of the present invention will be described withreference to the accompanying drawings. Referring to FIGS. 1 through 5,a first embodiment will be described.

[0059] A process chamber 2 of an etching treatment apparatus 1 isassembled by alumite-processed aluminium plates. It is earthed and asuscepter 5 insulated by an insulating plate 3 is arranged in it. Thesuscepter 5 is supported by its bottom through the insulating plate 3and a support 4.

[0060] A coolant chamber 6 is formed in the suscepter support 4. It iscommunicated with a coolant supply supply (not shown) through inlet andoutlet pipes 7 and 8 and coolant such as liquid nitrogen is circulatedbetween it and the coolant supply supply.

[0061] An internal passage 9 is formed in a suscepter assembly whichcomprises the insulating plate 3, the support 4, the suscepter 5 and anelectrostatic chuck 11, and heat exchanger gas such as helium gas issupplied from a gas supply supply (not shown) to the underside of awafer W through it.

[0062] The top center portion of the suscepter 5 is swelled and theelectrostatic chuck 11, same in shape as the wafer W, is mounted on theswelled portion of the suscepter 5. A conductive layer 12 of theelectrostatic chuck 11 is sandwiched between two sheets of highmolecular polyimide film. It in connected to a 1.5 kV DC high voltagepower supply 13 arranged outside the process chamber 2.

[0063] A focus ring 14 is arranged on the top of the suscepter 5 alongthe outer rim thereof, enclosing the wafer W. It is made of insulatingmaterial not to draw reactive ions.

[0064] An upper electrode 21 is opposed to the top of the suscepterassembly. Its electrode plate 24 is made of SiC or amorphous carbon andits support member 25 is made by an alumite-process aluminium plate. Itsunderside is separated from the wafer W an the suscepter assembly byabout 15-20 mm. It is supported by the top of the process chamber 2through an insulating member 22. A plurality of apertures 23 are formedin its underside.

[0065] A gas inlet 26 is formed in the center of the support 25 and agas inlet pipe 27 is connected to it. A gas supply pipe 28 is connectedto the gas inlet pipe 27. The gas supply pipe 28 is divided into threewhich are communicated with process gas supply sources 35, 36 and 37,respectively. The first one is communicated with the CF₄ gas supplysource 35 through a valve 29 and a mass flow controller 32. The secondone with the O₂ gas supply supply 36 through a valve 30 and a mass flowcontroller 33. The third one with the N₂ gas supply supply 37 throughvalve 31 and a mass flow controller 34.

[0066] An exhaust pipe 41 is connected to the bottom of the processchamber 2. An exhaust pipe 44 is also connected to the bottom of anadjacent load lock chamber 43. Both of them are communicated with acommon exhaust mechanism 45 which is provided with a turbo molecularpump and the like. The load lock chamber 43 is connected to the processchamber 2 through a gate valve 42. A carrier arm mechanism 46 isarranged in the load lock chamber 43 to carry the wafers W one by onebetween the process chamber 2 and the load lock chamber 43.

[0067] A high frequency power applier means for generating plasma in theprocess chamber 2 will be described.

[0068] A first oscillator 51 serves to oscillate high frequency signalhaving a frequency of 800 kHz. A circuit extending from the oscillator51 to the lower electrode (or suscepter) 5 includes a phase controller52, an amplifier 53, a matching unit 54, a switch SW₁ and a feeder rod55. The amplifier 53 is an RF generator and the matching unit 54includes a decoupling capacitor. The switch SW₁ is connected to thefeeder rod 55. A capacitance 56 is arranged on an earthed circuit of thefeeder rod 55. The phase controller 52 houses a bypass circuit (notshown) and a changeover switch (not shown) therein to enable signal tobe sent from the first oscillator 51 to the amplifier 53 through thebypass circuit. High frequency signal oscillated is applied to thesuscepter 5 through the phase controller 52, the amplifier 53, thematching unit 54 and feeder rod 55.

[0069] On the other hand, a second oscillator 61 serves to oscillatehigh frequency signal having a frequency of 27 MHz. A circuit extendingfrom the oscillator 61 to the upper (or shower) electrode 21 includes anamplitude modulator 62, an amplifier 63, a matching unit 64, a switchSW₂ and a feeder rod 65. The amplitude modulator 62 is connected to asignal circuit of the second oscillator 61 and also to that of the firstoscillator 51. It houses a bypass circuit (not shown) and a changeoverswitch (not shown) in it to enable signal to be sent from it to theamplifier 63 through the bypass circuit. The amplifier 63 is an RPgenerator and the matching unit 64 includes a decoupling capacitor. Theswitch SW₂ is connected to the feeder rod 65. A capacitance 66 and aninductance 67 are arranged on an earthed circuit of the feeder rod 65.High frequency signal oscillated is applied to the upper electrode 21through the amplitude modulator 62, the amplifier 63, the matching unit64 and the feeder rod 65. High frequency signal having the frequency of800 kHZ can also be applied, as modulated wave, to the amplitudemodulator 62.

[0070] The reason why the earthed circuit of the feeder rod 55 includesno inductance resides in that the electrostatic chuck 11, the gaspassage 9, the coolant chamber 6, lifter pins (not shown) and the likeare included in the lower electrode signal transmission circuit, thatthe feeder rod 55 itself is long, and that the suscepter 5 itself haslarge inductance accordingly.

[0071] The amplifiers 51 and 64 are arranged independently of the other.Therefore, voltages applied to the upper electrode 21 and the suscepter5 can be changed independently of the other.

[0072] Referring to FIG. 2, it will be described how silicon oxide film(SiO₂) on the silicon wafer W is plasma-etched.

[0073] Both of the load lock chamber 43 and the process chamber 2 areexhausted to substantially same internal pressure. The gate valve 42 isopened and the wafer W is carried from the load lock chamber 43 into theprocess chamber 2 (step S1). The gate valve 42 is closed and the processchamber 2 is further exhausted to set its internal pressure in a rangeof 10-250 mTorr (step S2).

[0074] The valves 29 and 30 are opened, and CF₄ and O₂ gases areintroduced into the process chamber 2. Their flow rates are controlledand they are mixed at a predetermined rate. The (CF₄+O₂) mixed gases aresupplied to the wafer W through apertures 23 of the upper showerelectrode 21 (step S3). When the internal pressure in the chamber 2becomes stable at about 1 Pa, high frequency voltages are applied to theupper and lower electrodes 21 and 5 to generate plasma between them.

[0075] Frequencies of high frequency power applied to the upper andlower electrodes 21 and 5 to generate plasma are controlled as follows(step S4).

[0076] The switches SW₁ and SW₂ are opened to disconnect (OFF) thecapacitance 56 from the feeder rod 55 and the capacitance 66 and theinductance 67 from the feeder rod 65. When the oscillators 61, 51, theamplitude modulator 62 and the amplifiers 63, 53 are made operativeunder this state, high frequency power having a certain waveform isapplied to the upper electrode 21. High frequency power having afrequency same as or higher than the higher one of upper ion transitfrequencies characteristic of CP₄ and O₂ gases is applied to the upperelectrode 21. High frequency power having a waveform shown in FIG. 3,for example, is applied to the upper electrode 21. Plasma is thusgenerated.

[0077] On the other hand, high frequency power having a certain waveformis applied to the lower electrode 5 by the oscillator 51. High frequencypower having a frequency same as or lower than the lower one of iontransit frequencies characteristic of CF₄ and O₂ gases is applied to thelower electrode S. High frequency power having a waveform shown in FIG.4, for example, is applied to the lower electrode. Ions in plasma arethus accelerated and drawn to the wafer W. passing through the plasmasheath, to thereby act on the wafer W.

[0078] The high frequency by which plasma is generated has the waveformshown in FIG. 3 in this case. Therefore, the dissociation of gasesintroduced into the process chamber 2 is not advanced to an extentgreater than needed. In addition, the frequency of 800 kHz by which ionsin plasma are accelerated and drawn to the wafer W can be controlled inphase by the phase controller 52. Ions can be thus drawn to the wafer Wbefore the dissociation of gases progresses to the extent greater thanneeded. When ions most suitable for etching are generated, therefore,they can be made incident onto the wafer W. When they are caused to acton the wafer W while cooling it, therefore, anisotropic etching having ahigh aspect rate can be realized.

[0079] The phase control of the high frequency power (frequency: 800kHz) applied to the lower electrode may be based on a state under whichthe dissociation of gases does not progress to the extent greater thanneeded or a state under which the dissociation of gases progresses tothe final stage, they are then combined again and become radicalssuitable for etching.

[0080] Further, it may be arranged that a dummy wafer DW is used andthat the treatment is carried out while confirming the extent to whichthe phase of the high frequency 800 kHz is shifted. The timing at whichthe phase of the high frequency 800 kHz is shifted may be previously setin this case, depending upon kinds of process gases, etching, coatingand the like.

[0081] When the end point of anisotropic etching is detected (step S5),exhaust, process gas introducing and plasma control steps S6, S7 and S8are successively carried out to isotropically etch film on the wafer W.The exhaust step S6 is substantially same as the above-described one S2.At the process gas introducing step S7, C₄F₈, CH3, Ar and CO gases, forexample, different from those at the above-described step S3, aresupplied to the process chamber 2.

[0082] At the plasma control step S8, plasma is controlled substantiallyas seen at the above-described step S4. When the end point of isotropicetching is detected (step S9), the applying of the high frequency poweris stopped and the process chamber 2 is exhausted while supplyingnitrogen gas into it (step S10). The gate valve 42 is opened and thewafer W is carried from the process chamber 2 into the load lock chamber43 (step S11).

[0083] Referring to FIG. 5, the plasma control steps S4 and S8 will bedescribed in more detail.

[0084]FIG. 5 is a graph showing ion transit frequency zonescharacteristic of three kinds of gases A, B and C, in which frequenciesare plotted on the vertical axis. An ion transit frequency zone Az ofgas A extends from an upper end Au to a lower end Al, an ion transitfrequency zone Bz of gas B from an upper end Bu to a lower end Bl, andan ion transit frequency zone Cz of gas C from an upper end Cu to alower end Cl. CHF₃ or CO gas is cited as gas A. Ar gas is cited as gasB. CP₄, C₄F₈ or O₂ gas is cited as gas C. At least one or more gasesselected from the group consisting of CF₄, C₄F₈, CHF₃, Ar, O₂ and COgases are used as process gas. In short, process gas may be one of themor one of mixed gases (CH₃+Ar+O₂), (CRF₃+CO+O₂), (C₄F₈+Ar+O₂),(C₄F₈+CO+Ar+O₂) and (CF₄+CHF₃).

[0085] When mixed gases of A, B and C are used as process gas, the highfrequency power applied to the upper electrode has a frequency higherthan the highest one Bu of upper ion transit frequencies Au, Bu and Cuand the high frequency power applied to the lower electrode has afrequency lover than the lowest one Cl of lower ion transit frequenciesAl, Bl and Cl.

[0086] Another etching treatment method conducted using theabove-described etching treatment apparatus 1 will be described.

[0087] The switches SW₁ and SW₂ are closed or turned on to connect thesignal transmission circuits to their earthed circuits. High frequencysignal (frequency: 800 kHz) is amplified directly by the amplifier 53,bypassing the phase controller 52, and applied to the suscepter 5through the matching unit 54. On the other hand, high frequency signal(frequency: 27 MHz) is amplified directly by the amplifier 63, bypassingthe amplitude modulator 62, and applied to the upper electrode 21 viathe matching unit 64 and the feeder rod 65.

[0088] Conventionally, the matching unit arranged on the side of thesuscepter is matched relative to the high frequency of 800 kHz but itbecomes high in impedance relative to the high frequency of 27 MHzapplied from the upper electrode, thereby making it difficult for thehigh frequency applied from the upper electrode to flow to thesuscepter. Plasma is thus scattered, so that the plasma densitydecreases.

[0089] In the apparatus 1, however, the capacitance 56 is arrangedbetween the feeder rod and the ground. A DC resonance circuit can bethus formed relative to the high frequency applied from the upperelectrode. When the value of the capacitance 56 is adjusted, consideringthe constant of a distributed constant circuit, therefore, compositeimpedance can be made smaller than several Ω to thereby make it easy forthe high frequency applied from the upper electrode to flow to thesuscepter 5. Therefore, current density can be raised and plasma densitythus attained can also be raised.

[0090] On the other hand, the capacitance 66 and the inductance 67 areattached to the feeder rod 65 arranged on the side of the upperelectrode 21. Therefore, a DC resonance circuit is also providedrelative to the high frequency of 800 kHz, thereby making it easy forthe high frequency 800 kHz applied to the side of the suscepter 5 toflow to the upper electrode 21. The incidence of ions in plasma onto thewafer W is promoted accordingly.

[0091] Although high frequency power having the frequency 27 MHz hasbeen applied to the upper electrode 21 and high frequency power havingthe frequency 800 kHz to the lower electrode 5 in the above-describedembodiment, other frequencies may be set, depending upon kinds ofprocess gas.

[0092] It is desirable that high frequency power applied to the lowerelectrode 5 has a frequency lower than the inherent lower ion transitfrequency or lower than 1 MHz and that high frequency power applied tothe upper electrode 21 has a frequency higher than the inherent upperion transit frequency or higher than 10 MHz. When so arranged, ions aremore efficiently accelerated with a smaller high frequency power and thefollow-up of ions in the plasma sheath to bias frequencies becomesstable even when the rate of gases mixed and the degree of vacuum in theprocess chamber are a little changed. Therefore, ions can be madeincident onto the wafer without scattering in the plasma sheath, therebyenabling a finer work to be achieved at high speed.

[0093] According to the present invention, the follow-up of ions is moreexcellent due to the high frequency power applied to he first electrodeand they can be more efficiently accelerated with a smaller power. Inaddition, plasma itself can be kept stable. A more stable treatment canbe thus realized even when the degree of vacuum in the process chamberand the rate of gases mixed change.

[0094] Further, when the dissociation is controlled not to progress tothe extent greater than needed and the phase of the high frequency powerapplied to the first electrode is also controlled, ions or radicalsneeded for the treatment can be created at a desired timing and they canbe made incident onto the wafer. Anisotropic etching treatment having ahigh aspect rate can be thus attained. In addition, damage applied tothe wafers can be reduced. Further, plasma density can be made highwithout raising the high frequency power and its frequency, and ioncontrol can be made easier.

[0095] A second embodiment will be described referring to FIG. 6. Samecomponents as those in the above-described first embodiment will bementioned only when needed.

[0096] An etching treatment apparatus 100 has, as high frequency powerapplier mans, two high frequency power supplies 141, 151 and atransformer 142. The primary side of the transformer 142 is connected tothe first power supply 141 and then earthed. Its secondary side isconnected to both of the upper and lower electrodes 21 and 105. A firstlow pass filter 144 is arranged between the secondary side and the upperelectrode 21 and a second low pass filter 145 between the secondary sideand the lower electrode 105. The first power supply 141 serves to applyhigh frequency power having the relatively low frequency such as 380 kHzto the electrodes 105 and 21. When silicon oxide (SiO₂) film is to beetched, it is optimum that a frequency f₀ of high frequency powerapplied from the first power supply 141 is 380 kHz and when polysilicon(poly-Si) film is to be etched, it is preferably in a range of 10 kHz-5MHz.

[0097] The transformer 142 has a controller 143, by which the power ofthe first power supply 141 is distributed to both electrodes 105 and 21at an optional rate. For example, 400 W of full power 1000 W can beapplied to the suscepter 105 and 600 W to the upper electrode 21. Inaddition, high frequency powers whose phases are shifted from each otterby 180° are applied to the suscepter 105 and the upper electrode 21.

[0098] The second power supply 151 serves to apply high frequency powerhaving the high frequency such as 13.56, for example, to the upperelectrode 21. It in connected to the upper electrode 21 via a capacitor152 and then earthed. This plasma generating circuit is called P modeone. It is optimum that a frequency f₁ of high frequency power appliedfrom it is 13.56 MHz, preferably in a range of 10-100 MHz.

[0099] It will be described how silicon oxide film (SiO₂) on the siliconwafer W is etched by the above-described etching apparatus 100.

[0100] The wafer W is mounted on the suscepter 105 and sucked and heldthere by the electrostatic chuck 11. The process chamber 102 inexhausted while introducing CF₄ gas into it. After its internal pressurereaches about 10 mTorr, high frequency power of 13.56 MHz is appliedfrom the second power supply 151 to the upper electrode 21 to make CF₄gas into plasma and dissociate gas molecules between the upper electrode21 and the suscepter 105. On the other hand, high frequency power of 380kHz is applied from the first power supply 141 to the upper and lowerelectrodes 21 and 105. Ions and radicals such as fluoric ones inplasma-like gas molecules are thus drawn to the suscepter 105, therebyenabling silicon oxide film on the wafer to be etched.

[0101] The generating and keeping of plasma itself are attained in thiscase by the high frequency power having a higher frequency and appliedfrom the second power supply 151. Stable and high density plasma can bethus created. In addition, activated species in this plasma arecontrolled by the high frequency power of 380 kHz applied to the upperand lower electrodes 21 and 105. Therefore, a more highly selectiveetching can be applied to the wafer W. Ions cannot follow up to the highfrequency power which has the frequency of 13.56 MHz and by which plasmais generated. Even when the output of the power supply 131 is made largeto generate high density plasma, however, the wafers w cannot bedamaged.

[0102] The first and second low pass filters 144 and 145 are arranged onthe secondary circuit of the transformer 142. This prevents the highfrequency power having the frequency of 13.56 MHz and applied from thesecond power supply 151 from entering into the secondary circuit of thetransformer 142. Therefore, the high frequency power having thefrequency of 13.56 MHz does not interfere with the one having thefrequency of 380 kHz, thereby making plasma stable. Blocking capacitorsmay be used instead of the low pass filters 144 and 145. Although highfrequency powers have been continuously applied to the electrodes in theabove case, modulation power which becomes strong and weak periodicallymay be applied to the electrodes 21 and 105.

[0103] A third apparatus 200 will be described with reference to FIG. 7.Same components as those in the above-described first and secondembodiments will be mentioned only when needed.

[0104] A high frequency power circuit of this apparatus 200 is differentfrom that of the second embodiment in the following points: A suscepter205 of the apparatus 200 is not earthed; no low pass filter is arrangedon the secondary circuit of a transformer 275; and a second transformer282 is arranged on the circuit of a second power supply 281.

[0105] The second power supply 281 serves to generate high frequencypower of 3 MHz. It is connected to the primary side of the transformer282, whose secondary side are connected to upper and lower electrodes 21and 205. A controller 293 which controls the distribution of power isalso attached to the secondary side of the transformer 282.

[0106] It will be described how the etching treatment is carried out bythe apparatus 200.

[0107] High frequency powers of 3 MHz whose phases are shifted from eachother by 180° are applied from the power supply 281 to the suscepter 205and the upper electrode 21 to generate plasma between them. At the sametime, high frequency powers of 380 kHz whose phases are shifted fromeach other by 180° are applied from a power supply 274 to them. Ions inplasma generated are thus accelerated to enter into the wafer W.

[0108] Further, the two high frequency power supplies 274 and 281 in thethird apparatus are arranged independently of the other. In short, theyare of the power split type. Therefore, they do not interfere with eachother, thereby enabling a more stable etching treatment to be realized.

[0109] Furthermore, high frequency powers are supplied from the twopower supplies 274 and 281 to both of upper and lower electrodes 21 and205, respectively. The flow of current can be thus concentrated on anarrow area between the upper 21 and the lower electrode 205. As theresult, a high density plasma can be generated and the efficiency ofcontrolling ions in plasma can be raised.

[0110] A fourth embodiment will be described, referring to FIGS. 8through 12. Same components as those in the above-described embodimentswill be mentioned only when needed.

[0111] As shown in FIG. 8, an etching apparatus 300 has a cylindrical orrectangular column-like air-tight chamber 302. A top lid 303 isconnected to the side wall of the process chamber 302 by hinges 304.Temperature adjuster means such as a heater 306 is arranged in asuscepter 305 to adjust the treated face of a treated substrate W to adesired temperature. The heater 306 is made, for example, by inserting aconductive resistance heating unit such as tungsten into an insulatingsintered body made of aluminium nitride. Current is supplied to thisresistant heating unit through a filter 310 to control the temperatureof the wafer W in such a way that the treated face of the wafer W israised to a predetermined temperature.

[0112] A high frequency power supply 319 is connected to the suscepter305 through a blocking capacitor 318.

[0113] When the wafer W is to be etched, the high frequency power of13.56 MHz is applied from the power supply 319 to the suscepter 305.

[0114] The suscepter 305 is supported by a shaft 321 of a liftermechanism 320. When the shaft 321 of the lifter mechanism 320 isextended and retreated, the suscepter 305 is moved up and down. Abellows 322 is attached to the lower end of the suscepter 305 not toleak gases in the process chamber 302 outside.

[0115] Reaction products deposit in the process chamber 302. A ring 325is freely detachably attached to the outer circumference of thesuscepter 305. It is made preferably of PTFE (teflon), PFA, polyimide orPBI (polybenzorimdazole). It may also be made of such a resin that hasinsulation in a temperature range of common temperature—500° C. or ofsuch a metal like aluminium that has insulating film on its surface. Abaffle plate 326 is made integral to it. A plurality of holes 328 areformed in the baffle plate 326. They are intended to adjust the flow ofgases in the process chamber 302, to make its exhaust uniform, and tomake a pressure difference between the treatment space and a spacedownstream the flow of gases. A top portion 327 of the ring 325 is bentinwards, extending adjacent to the electro-static chuck 11, to make thetop of the suscepter 305 exposed as small as possible.

[0116] An upper electrode 330 is arranged above the suscepter 305. whenthe etching treatment is to be carried out, the suscepter 305 is liftedto adjust the interval between the suscepter 305 and the upper electrode330. The upper electrode 330 is made hollow and a gas supply pipe 332 isconnected to this hollow portion 331 to introduce CH₄ gas and othersfrom a process gas supply supply 333 into the hollow portion 331 througha mass flow controller (MFC) 334. A diffusion plate 335 is arranged inthe hollow portion 331 to promote the uniform diffusion or scattering ofprocess gases. Further, a process gas introducing section 337 having aplurality of apertures 336 is arranged under the diffusion plate 335. Anexhaust opening 340 which is communicated with an exhaust systemprovided with a vacuum pump and others is formed in the side wall of theprocess chamber 302 at the lower portion thereof to exhaust the processchamber 302 to an internal pressure of 0.5 Torr, for example.

[0117] When the wafer W is etched in the process chamber 302, reactionproducts are caused and they adhere to the ring 325 and the baffle plate326, leaving the outer circumference of the suscepter 305 substantiallyfree from them. When the etching treatment is finished, the wafer W iscarried out of the process chamber 302 into the load lock chamber 43. Anext new wafer W is then carried from the load lock chamber 43 into theprocess chamber 302 and etched in it. When this etching treatment isrepeated many times, a lot of reaction products adhere to the ring 325.

[0118] As shown in FIG. 9, the top lid 303 of the process char 302 isopened and the ring 325 is detached from the suscepter 305. Reactionproducts are then removed from the ring 325 by cleaning.

[0119] The time at which the ring 325 must be cleaned is determined asfollows:

[0120] the number of particles adhering to the wafer W which has beentreated by the apparatus 300 is counted and when it becomes larger thana predetermined value;

[0121] the number of particles scattering in the atmosphere exhaustedfrom the apparatus 300 and/or at least in one or more areas in theexhaust pipe is counted and when it becomes larger than a predeterminedvalue;

[0122] when predetermined sheets of the wafer W have been treated in theapparatus 300; and

[0123] when the total of hours during which plasma has been generated orthe plasma treatment has been carried out reaches a predetermined value.

[0124] Dry or wet cleaning is used. The dry cleaning is carried out insuch a way that ClF₃, CF₄ or NF₃ gas is blown to the ring 325 which isleft attached to the suscepter 305 or which is detached from thesuscepter 305 and left outside the process chamber 302, as shown in FIG.10.

[0125] On the other hand, the wet cleaning is carried out in such a waythat the ring 325 to which reaction products have adhered is immersed incleaning liquid 351 in a container 350, as shown in FIG. 11. IPA(isopropyl alcohol), water or fluorophosphoric acid is used as cleaningliquid 351. The ring 325 from which reaction products have been removedby the dry or wet cleaning is again attached to the suscepter 305 andthe plasma treatment is then repeated.

[0126] When the wafers W are to be etched, plural rings 325 arepreviously prepared relative to one suscepter 305. If so, cleaned onecan be attached to the suscepter 305 while cleaning the other.

[0127] The dry or wet cleaning can be appropriately used to removereaction products from the ring 325. When the dry cleaning is comparedwith the wet one, however, the former is easier in carrying out it butits cleaning is more incomplete. To the contrary, the latter is moreexcellent in cleaning the ring 325 but its work is relatively moretroublesome. Therefore, it is desirable that the wet cleaning isperiodically inserted while regularly carrying out the dry cleaning.

[0128] The baffle plate will be described referring to FIGS. 12 and 13.

[0129] As shown in FIG. 12, it is preferable that an effective diameterD₁ is set not larger than a diameter D₂. The effective diameter D₁represents a diameter of that area where the process gas jettingapertures 336 are present, and the diameter D₂ denotes that of the waferW in this case. When the effective diameter D₁ is set in this manner, ahigh efficient etching can be attained in the process chamber 302. It isthe most preferable that the effective diameter D₁ is set to occupyabout 90g of the diameter D₂.

[0130] Providing that the underside 338 of the upper electrode has adiameter D₃, the effective diameter D₁, the diameter D₂ and the diameterD₃ meet the following inequality (1).

D₁<D₂<D₃  (1)

[0131] When the ring the whole of which is made of insulating materialis used as it is, the effective area of the lower electrode becomessubstantially smaller than that of the upper electrode, thereby makingplasma uneven. This problem can be solved when the effective area of thelower electrode is made same as that of the upper electrode or when itis made larger than that of the upper electrode.

[0132] As shown in FIG. 13, the baffle plate 326 is made integral to thering 325. It is divided into a portion 360 equal to the diameter D₄ andanother portion 361 larger than it, and the inner portion 360 is made ofmetal such as aluminium and stainless steel while the outer portion 361of PTFE (teflon), PPA, polyimide, PBI (polybenzoimidazole), otherinsulating resin or alumite-processed aluminium.

[0133] The diameter D₄ is made same as or larger than the diameter D₃.At least the inner portion 360 of the baffle plate 326 is positionedjust under the upper electrode 330. The ring 326 is divided into anupper half 363 and a lower half 364, sandwiching an insulator 362between them. The upper half 363 is made of metal such as aluminium andstainless steel and it is made integral to the inner portion 360 of thebaffle plate 326. A power supply 319 which serves to apply highfrequency power to the suscepter 305 is connected to these inner portion360 of the baffle plate 326 and upper half 363 of the ring 325 by a lead367 via a blocking capacitor 318. At least those portions (the innerportion 360 of the baffle plate and the upper half 363 of the ring)which are positioned just under the upper electrode 330 are made same inpotential. In order to make it easy to exchange the ring 325, it ispreferable that the lead 367 is connected to the upper half 363 of thering or the inner portion 360 of the baffle plate 326 by aneasily-detached socket 368. A lower suscepter 365 is insulated from theupper one 305 by an insulating layer 366. The lower half 364 of the ringis also therefore insulated from the upper half 363 thereof by theinsulator 362.

[0134] When at least that portion of the baffle plate 326 which ispositioned just under the upper electrode 330 is made same in potentialas the suscepter 305, as described above, plasma can be made uniform.

[0135] Referring to FIGS. 14 and 15, it will be described how the sideopening 41 of the process chamber 302 through which the wafer W iscarried in and out is opened and closed as the suscepter is moved up anddown.

[0136] The ring 325 provided with the baffle plate 326 encloses thesuscepter 305. The lifter means 320 is arranged under the process car302 and the suscepter 305 is supported by the shaft 321 of the liftermeans 320.

[0137] When the suscepter 305 is moved down, as shown in FIG. 14, thebaffle plate 326 is positioned lower than the side opening 41. When itis moved up, as shown in FIG. 15, the baffle plate 326 is positionedhigher than the side opening 41.

[0138] When the suscepter 305 is moved down and the baffle plate 326 ispositioned lower than the side opening 41, therefore, the wafer W can befreely carried in and out of the process chamber 302 through the sideopening 41. When the baffle plate 326 is positioned higher than the sideopening 41 at the time of etching treatment, however, the side opening41 is shielded from the process space between the upper and the lowerelectrode, thereby preventing plasma from entering into the side opening41.

[0139] As shown in FIG. 16, it may be arranged that a shielding plate370 is attached to the outer circumference of the baffle plate 326 andthat the side opening 41 is closed by the shielding plate 370 when thesuscepter 305 is moved up. Particularly, the side opening 41 is toonarrow for hands to be inserted. Therefore, inert gas may be supplied,as purge gas, into a clearance 371 between the shielding plate 370 andthe inner face of the process chamber 302 not to cause process gases toenter into the side opening 41. Similarly, purge gas may also besupplied into a clearance 372 between the wafer-mounted stage 305 andthe upper half 363 of the ring 325.

[0140] The side opening 41 may be closed by a shielding plate 373attached to the outer circumference of the baffle plate 326, as shown inFIG. 17, when the baffle plate 326 is lifted half the side opening 41.

[0141] Referring to FIGS. 18 through 28, the cleaning of a fifth CVDapparatus will be described. Same components an those in theabove-described embodiments will be mentioned only when needed.

[0142] A CVD apparatus 500 has a process chamber 502 which can beexhausted vacuum. A top lid 503 is connected to the side wall of theprocess chamber 502 by hinges 505. A shower head 506 is formed in thecenter portion of the top lid 503 at the underside thereof. A processgas supply pipe 507 is connected to the top of the shower head 506 tointroduce mixed gases (SiH₄+H₂) from a process gas supply 508 into theshower head 506 through a mass flow controller (MFC) 510. A plurality ofgas jetting apertures 511 are formed in the bottom of the shower head506 and process gases are supplied to the wafer W through theseapertures 511.

[0143] An exhaust pipe 516 which is communicated with a vacuum pump 515is connected to the side wall of the process chamber at the lowerportion thereof. A laser counter 517 which serves to count the number ofparticles contained in the gas exhausted from the process chamber 502 isattached to the exhaust pipe 516. The process chamber 502 isdecompressed to about 10⁻⁶ Torr by the exhaust means 515.

[0144] The process chamber 502 has a bottom plate 521 supported by asubstantially cylindrical support 520 and cooling water chambers 522 areformed in the bottom plate 521 to circulate cooling water suppliedthrough a cooling water pipe 523 through them.

[0145] A suscepter 525 is mounted on the bottom plate 521 through abeater 526 and these heater 526 and the wafer-mounted stage 525 areenclosed by a heat insulating wall 527. The heat insulating wail 527 hasa mirror-finished surface to reflect heat radiated from around. Theheater 526 is heated to a predetermined temperature or 400-2000° C. byvoltage applied from an AC power supply (not shown). The wafer W on thestage 525 is heated to 800° C. or more by the heater 526.

[0146] An electrostatic chuck 530 is arranged on the top of thewafer-mounted stage 525. It comprises polyimide resin films 531, 532 anda conductive film 533. A variable DC voltage supply (not shown) isconnected to the conductive film 533.

[0147] A detector section 538 of a temperature sensor 537 is embedded inthe suscepter 525 to successively detect temperature in thewafer-mounted stage 525. The power of the AC power supply which isSupplied to the heater 526 is controlled responsive to signal appliedfrom the temperature sensor 537. A lifter 541 is connected to thesuscepter 525 through a member 543 to move it up and down. Thoseportions of a support plate 546 through which support poles 544 and 545are passed are provided with bellows 547 and 548 to keep the processchamber 502 air-tight.

[0148] A cover 560 is freely detachably attached to the shower head 506.It is made of material of the PTFE (teflon) group, PFA, polyimide, PEI(polybenzoimidazole) or polybenzoazole, which are insulators and heatresistant. In the case of the plasma CVD apparatus, the wafer-mountedstage 525 is heated to about 350-400° C. at the time of plasma processand in the case of the heat CVD apparatus, it is usually heated higherthan 650° C. or to about 800° C. The cover 560 is therefore made of sucha material that can resist this radiation heat.

[0149] As shown in FIG. 19, a large-diameter opening 563 is formed in abottom 561 of the cover 560. When the cover 560 is attached to theshower head 506, the gas jetting apertures 511 of the shower head 506appear in the opening 563.

[0150] As shown in FIG. 20, a plurality of apertures 565 may also beformed in the cover 560. These apertures 565 are aligned with those ofthe shower head 506 in this case.

[0151] As shown in FIG. 21, recesses 570 may be formed in the outercircumference of the shower head 506 while claws 571 are formed on aninner circumference 562 of the cover 506, as shown in FIG. 22. The claws571 are fitted into recesses 570 in this case while elasticallydeforming the cover 560. The three claws 571 are arranged on the innercircumference 562 of the cover 560 at a same interval, as shown in FIG.22.

[0152] As shown in FIG. 23, the cover 560 may be attached to the showerhead 506 in such a way that bolts 575 are screwed into recesses 573 ofthe shower head 506 through a cover side 562.

[0153] It will be described how upper electrode cover is cleaned.

[0154] When mixed gases (SiH₄+H₂), for example, are introduced into theprocess chamber 502 to form film on the wafer W, reaction productsadhere to the upper electrode cover 560. As shown in FIG. 24, the toplid 503 is opened and the cover 560 is detached from the shower head506. The cover 560 is then immersed in cleaning liquid 581 in acontainer 580 (wet cleaning). Or the dry cleaning may be conducted insuch a way that cleaning gas such as ClF₃, CP₄ or NF₃ gas is introducedinto the process chamber 502 while keeping the cover 560 attached to theshower head 506.

[0155] The time at which the cleaning must be conducted is determined asfollows. The number of particles contained in the gas exhausted throughthe exhaust pipe 516 is counted by the counter 517 and when it becomeslarger than a limit value, the cleaning of the cover 560 must bestarted.

[0156] As shown in FIG. 26, the underside of the top lid 503 may becovered by a cover 585, in addition to the shower head 506. Or the innerface of the process chamber 502 may be covered by a cover 586, inaddition to the shower head 506, as shown in FIG. 27. An opening 587 isformed in the cover 586 in this case, corresponding to the side opening41 of the process chamber 502. Or a cover 590 having a curved bottom 591may be used, as shown in FIG. 28.

[0157] A sixth embodiment will be described referring to FIGS. 29through 34. Same components as those in the above-described embodimentswill be mentioned only when needed.

[0158] As shown in FIG. 29, a magnetron type plasma etching apparatus600 has a rotary magnet 627 above a process chamber 602. Upper and lowerelectrodes 624 and 603 are opposed in the process chamber 602.

[0159] Process gases are introduced from a gas supply supply 629 to thespace between the upper and the lower electrode through an MFC 630. Therotary magnet 627 serves to stir plasma generated between both of theelectrodes 603 and 624.

[0160] A suscepter assembly comprises an insulating plate 604, a coolingblock 605, a heater block 606, an electrostatic chuck 608 and a focusring 612. A conductive film 608 c of the electrostatic chuck 608 isconnected to a filter 610 and a variable DC high voltage supply 611 by alead 609. The filter 610 is intended to cut high frequencies. Aninternal passage 613 is formed in the cooling block 605 and liquidnitrogen is circulated between it and a coolant supply supply (notshown) through pipes 614 and 615. A gas passage 616 is opened at tops ofthe suscepter 603, the heater 617 and the cooling block 605, passingthrough the suscepter assembly. The base end of the gas passage 616 iscommunicated with a heat exchanger gas supply supply (not shown) tosupply heat exchanger gas such as helium gas to the underside of thewafer W through it. The heater block 606 is arranged between thesuscepter 603 and the cooling block 605. It is shaped like a band-likering and it is several mm thick. It is a resistant heating unit. It isconnected to a filter 619 and a power supply 620.

[0161] Inner and outer pipes 621 a and 521 b are connected to thesuscepter 603 and the process chamber 602. They are conductive doublepipes, the outer one 621 a of which is earthed and the inner one 621 bof which is connected to a high frequency power supply 623 via ablocking capacitor 622. The high frequency power supply 623 has anoscillator for oscillating the high frequency of 13.56 MHz. Inert gas isintroduced from a gas supply supply (not shown) into a clearance betweenthe inner 621 a and the outer pipe 621 b and also into the inner pipe621 b.

[0162] Except the upper electrode, the inner faces of the top of theprocess car 602 is covered by an insulating protection layer 625, 3 mmor more thick. similarly, the inner face of its side wall is covered byan insulating protection layer 626, 3 mm or more thick.

[0163] In the conventional magnetron type plasma etching apparatus, theflow of electrons tends to gather near the inner wall of the processchamber, as shown in FIG. 34. The flow of plasma is thus irradiated in adirection W. that is, to the side wall of the process chamber, therebydamaging it. In the above-described apparatus 600, however, the sidewail of the process chamber 602 is covered by the insulating protectionlayer 626 so that it can be protected.

[0164] Process gas supply and exhaust lines or systems of the apparatus600 will be described.

[0165] A process gas supply pipe 628 is connected to the side wall ofthe process chamber 602 at the upper portion thereof and CF₄ gas isintroduced from a process gas supply 629 into the process chamber 602through it. An exhaust pipe 633 is also connected to the side wall ofthe process chamber 602 at the lower portion thereof to adjust theprocess chamber 602 by an exhaust means 631, which is provided with avacuum pump. A valve 632 is attached to the exhaust pipe 633.

[0166] As shown in FIG. 30, a baffle plate 635 is arranged between theouter circumference of the suscepter 603 and the inner wall of theprocess chamber 602. Plural holes 634 are formed in the baffle plate 635to adjust the flow of exhausted air or gas.

[0167] As shown in FIG. 31, each hole 634 is tilted. Therefore, theconductance of gas rises when it passes through the holes 634 and thegradient of electric field becomes gentle accordingly. This preventsdischarge from being caused in the holes 634 and plasma from flowinginward under the baffle plate 635.

[0168] As shown in FIG. 32, holes 634 a, 634 b, 634 c and 634 d eachhaving a same pitch may be formed in plural baffle plates 635 a, 635 b,635 c and 635 d to form a step-like exhaust hole 634A. This exhaust hole634A can be formed when the baffle plates 635 a, 635 b, 635 c and 635 dare placed one upon the others in such a way that the holes 634 a, 634b, 634 c and 634 d are a little shifted from their adjacent ones. Whenthese exhaust holes 634A are formed, abnormal discharges in plasmageneration can be more effectively prevented In the conventionalapparatus, each hole 692 in the baffle plate extends only vertical, asshown in FIG. 33. Those holes 692 allow plasma to flow inward under thebaffle plate and abnormal discharges such as sparkles to be caused inthem, thereby causing metal contamination and particles. In theapparatus 600, however, the holes 634 are directed toward the exhaustopening 633. The reduction of exhaust speed can be thus prevented. Whenthe direction in which the turbo-pump 631 is driven is made reverse tothe flow of exhausted gas, that is, when it is made anticlockwise in acase where exhausted gas flows clockwise, the speed of exhausted gas canbe raise to a further extent.

[0169] A seventh embodiment will be described ref erring to FIGS. 35through 43. TEOS gas is used to form film on the wafer W in this seventhplasma CVD apparatus. Same components as those in the above-describedembodiments will be mentioned only when needed.

[0170] The plasma CVD apparatus 700 has a cylindrical or rectangularprocess chamber 710, in which a suscepter 712 is arranged to hold awafer W on it. It is made of conductive material such as aluminium andit is insulated from the wall of the process chamber 710 by aninsulating member 714. A heater 716 which is connected to a power supply718 is embedded in it. The wafer W on it is heated to about 300° C. (orfilm forming temperature) by the heater 716. The process chamber is ofthe cold wall type in this case, but it may be of the hot wall type. Theprocess chamber of the hot wall type can prevent gas from beingcondensed and stuck.

[0171] The electrostatic chuck 11 is arranged on the suscepter 712. Itsconductive film 12 is sandwiched between two sheets of film made ofpolybensoimidazole resin. A variable DC high voltage power supply 722 isconnected to the conductive film 12. A focus ring 724 is arranged on thesuscepter 712 along the outer rim thereof.

[0172] A high frequency power supply 728 is connected to the suscepter712 via a matching capacitor 726 to apply high frequency power having afrequency of 13.56 MHz or 40.68 MHz to the suscepter 712.

[0173] An upper electrode 730 serves as a plasma generator electrode andalso as a process gas introducing passage. It is a hollow aluminium-madeelectrode and a plurality of apertures 730 a are formed in its bottom.It has a heater (not shown) connected to a power supply 731. It can bethus heated to about 150° C. by the heater.

[0174] A process gas supply line or system provided with a vaporizer(VAPO) 732 will be described referring to FIGS. 35 and 36.

[0175] Liquid TEOS is stored in a container 734. At the film formingprocess, a liquid mass flow controller (LMFC) 736 is controlled by acontroller 758 to control the flow rate of liquid TEOS supplied from thecontainer 734 to the vaporizer 732.

[0176] As shown in FIG. 36, a porous and conductive heating unit 744 ishoused in a housing 742 of the vaporizer 732. The housing 742 has aninlet 738 and an outlet 740. The inlet 738 is communicated with theliquid supply side of the container 734. The outlet 740 is communicatedwith the hollow portion of the upper electrode 730.

[0177] The heating unit 744 is made of sintered ceramics in whichconductive material such as carbon is contained, and it is porous. It ispreferably excellent in workability and in heat and chemical resistance.Terminals 747 are attached to it and current is supplied from a powersupply 746 to it through them. When current is supplied to it, it isresistance-heated to about 150° C. Further, vibrators 748 are embeddedin the housing 742, sandwiching the heating unit 744 between them. It ispreferable that they are supersonic ones. The power supply 746 for theheating unit 744 and a power supply (not shown) for the vibrators 748are controlled by the controller 758.

[0178] It will be described how the vaporizer 732 is operated.

[0179] When liquid TEOS is supplied from the container 734 to thevaporizer 732, it enters into holes in the porous heating unit 744 andit is heated and vaporized. Because its contact area with the porousheating unit 744 becomes extremely large, its vaporized efficiencybecomes remarkably higher, as compared with the conventional vaporizers.

[0180] Further, vibration is transmitted from vibrators 748 to liquidTEOS caught by the heating unit 744 and in its holes. Heat transfer faceand liquid vibrations are thus caused. Therefore, the border layerbetween the heat transfer face of each hole in the heating unit 744 andliquid TEOS, that is, the heat resistance layer is made thinner. As theresult, convection heat transmission is promoted to further raise thevaporized efficiency of liquid TEOS.

[0181] According to the vaporizer in this case, gas-like TEOS is movedby pressure difference caused between the inlet 738 and the outlet 740and thus introduced into the process chamber 710 without using anycarrier gas.

[0182] A bypass 750 and a stop valve 752 may be attached to the passageextending from the outlet 740 of the vaporizer, as shown in FIG. 35. Thebypass 750 is communicated with a clean-up unit (not shown) via a bypassvalve 754. The clean-up unit has a burner and others to removeunnecessary gas components. Further, a sensor 756 is also attached tothe passage extending from the outlet 740 to detect whether or notliquid TEOS is completely vaporized and whether or not gases are mixedat a correct rate. Detection signal is sent from the sensor 756 to thecontroller 758.

[0183] The operation of the above-described CVD apparatus 700 will bedescribed.

[0184] The wafer w is carried into the process chamber 710 which hasbeen decompressed to about 1×10⁻⁴ several Torr, and it is mounted on thesuscepter 712. It is then heated to 300° C., for example, by the heater716. While preparing the process chamber 710 in this manner, liquid TEOSis vaporized by the vaporizer 732. High frequency power is applied fromthe high frequency power supply 728 to the lower electrode 712 togenerate reactive plasma in the process chamber. Activated species inplasma reach the treated face of the wafer W to thereby form P-TEOS(plasma-tetraethylorthosilicate) film, for example, on it.

[0185] Other vaporizers will be described referring to FIGS. 37 through41.

[0186] As shown in FIG. 37, a vaporizer 732A may be made integral to anupper electrode 730A of a process chamber 710A. It is attached integralto the upper electrode 730A at the upper portion thereof with anintermediate chamber 770 formed under it. Its housing 742A has a gasoutlet side 774 in which a plurality of apertures 772 are formed.

[0187] A gas pipe 776 is communicated with the intermediate chamber 770in the upper electrode 730A to introduce second gas such as oven andinert gases into it. A bypass 750A extends from that portion of theupper electrode 730A which is opposed to the gas pipe 776 to exhaustunnecessary gas from the upper electrode 730A. Further, plates 780 a,780 b and 780 c in which a plurality of apertures 778 a, 778 b and 778 care formed are arranged in the lower portion of the intermediate chamber770 with an interval interposed between them.

[0188] As shown in FIGS. 38 and 39, a liquid passage 782 is formed in aheating unit 744B in the case of a vaporizer 732B. It includes a centerpassage 782 a and passages 782 b radically branching from the centerpassage 782 a. When it is formed in the heating unit 744B in thismanner, it enables liquid to be uniformly distributed in the whole ofthe porous heating unit 744B, thereby raising gas vaporized efficiencyto a further extent.

[0189] After liquid is vaporized by a vaporizer 738C, two or more gasesmay be mixed, as shown in FIG. 40. A second gas supply opening 784 isarranged downstream the vaporizer 738C and second gas component such asoxygen and inert gases is supplied through it. A gas mixing duct 786extends downstream it and a bypass 750C having a bypass valve 754C, anda stop valve 752C are further arranged in the lower portion of the gasmixing duct 786. A strip-like mer 788 is housed in the gas mixing duct786 to form a spiral passage 790 in it. First and second gas componentsare fully mixed, while passing through the spiral passage 790, and theyreach a point at which the bypass 750 branches from the passageextending to the side of the process chamber.

[0190] In addition to TEOS (tetraethylorthosilicate), trichlorsilane(SiRC1 ₃), silicon tetrachloride (SiCl₄), pentaethoxytantalum (PEOTE:Ta(OC₂H₅)₅), pentamethoxytantalum (PNOTa: Ta(OCH₃)₅),tetrasopropoxytitanium (Ti(i-OC₃H₇)₄), tetradimethylaminotitanium(TDMAT: Ti(N(CH₃)₂)₄), tatraxisdiethylazinotitanium (TDEAT:Ti(N(C₂H₅)₂)₄), titanium tetrachloride (TiCl₄), Cu(HFA)₂ and Cu(DPM)₂may be used as liquid material to be vaporized. Further, Ba(DPX)₂/THFand Sr(DPX)₂/THF may be used as thin ferroelectric film foring material.Water (H₂O), ethanol (C₂H₅OH), tetrahydrfuran (THF: C₄H₈O) anddirmethylaluminiumhydride (DMAH: (CH₃)₂AlH) may also be used.

[0191] A vaporizer 819 may be attached to a batch type horizontal plasmaCVD apparatus 800, as shown in FIG. 41. This CVD apparatus 800 includesa process chamber 814 provided with an exhaust opening 810 and a processgas supply section 812, a wafer boat 816 and a heater means 818.Connected to the process gas supply section 812 are a process gas supplyline or system having a liquid container 815, a liquid mass flowcontroller 817 and a vaporizer 819. This vaporizer 819 is substantiallysame in arrangement as the above-described one 732.

[0192] As shown in FIG. 42, a conventional vaporizer 701 has a housing702 which is kept under atmospheric pressure and which is filled with aplurality of heat transmitting balls 703 each being made of material,excellent in heat transmission. These heat transmitting balls 703 areheated higher than the boiling point of liquid material by an externalheater means (not shown) to vaporize liquid material introduced frombelow. Carrier gas is introduced into the vaporizer 701 to carryvaporized process gases.

[0193] In the conventional vaporizer 701, however, gas flow rate becomesexcessive at the initial stage of gas supply, that is, overshooting iscaused. FIG. 43 is a graph showing how gas flow rates attained by theconventional and our vaporizers change at the initial stage of gassupply, in which time lapse is plotted on the horizontal axis and gasflow rates on the vertical axis. A curve P represents results obtainedby the conventional vaporizer and another curve Q those obtained by ourpresent vaporizer. As apparent from FIG. 43, gas flow rate overshoots apredetermined one v₁, in the case of the conventional vaporizer, afterthe lapse of 10-20 seconds since the supply of gas is started. In theabove-described vaporizer used by the present invention, however, itreaches the predetermined flow rate V₁ without overshooting it.

[0194] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details, representative devices,and illustrated examples shown and described herein. Accordingly,various modifications may be made without departing from the spirit orscope of the general inventive concept as defined by the appended claimsand their equivalents.

What is claimed is:
 1. A plasma treatment method of plasma-treating asubstrate, which is to be treated, under decompressed atmospherecomprising, the steps of: exhausting a process chamber so as todecompress the process chamber; mounting the substrate, which is to betreated, on a lower electrode; supplying a process gas to the substrateon the lower electrode through an upper electrode; applying highfrequency power, which has a first frequency f₁ lower than an inherentlower ion transit frequencies of said process gas, to the lowerelectrode; and applying high frequency power, which has a secondfrequency f₂ higher than an inherent upper ion transit frequencies ofsaid process gas, to the upper electrode, whereby a plasma is generatedin the process chamber and activated species influence the substrate tobe treated.
 2. The plasma treatment method according to claim 1 ,wherein said process gas is formed of a plurality of component gases,said first frequency f₁ is the lowest of the inherent lower ion transitfrequencies of said component gases, and said second frequency f₂ is thehighest of the inherent higher ion transit frequencies of said compositegases.
 3. The plan treatment method according to claim 1 , wherein thefirst frequency f₁ is lower that the second frequency f₂.
 4. The plasmatreatment method according to claim 1 , wherein the first frequency f₁is set lower than 1 MHz, and the second frequency f₂ is set higher than10 MHz.
 5. The plasma treatment method according to claim 4 , whereinthe first frequency f₁ is in a range of 100 kHZ-1 MHz, and the secondfrequency f₂ in a range of 10 MHz-100 MHz.
 6. The plasma treatmentmethod according to claim 1 , wherein high frequency components of saidfirst frequency f₁ are removed from said high frequency power applied tothe upper electrode.
 7. The plasma treatment method according to claim 1, wherein high frequency components of said second fluency f₂ areremoved from high frequency power entering into a pr supply circuitthrough plasma, a power supply circuit serving to apply said highfrequency power, which has the first frequency f₁, to the lowerelectrode.
 8. The plasma treatment method according to claim 1 , furthercomprising the steps of, applying high frequency power, which has afrequency same as the first frequency f₁ and which isamplitude-modulated, to the upper electrode.
 9. The plasma treatmentmethod according to claim 1 , further comprising the steps of, applyinghigh frequency power, which has a frequency same as the second frequencyf₂ and which is amplitude-modulated, to the lower electrode.
 10. Theplasma treatment method according to claim 8 , wherein amplitudemodulation is carried out to form one of sine, triangular, rectangularand sawtooth waveforms or their composite waveform.
 11. The plasmatreatment method according to claim 9 , wherein amplitude modulation iscarried out to form one of sine, triangular, rectangular and sawtoothwaveforms or their composite waveform.
 12. The plasma treatment methodaccording to claim 1 , wherein one or more gases selected from the groupconsisting of CF₄, C₄F₈, CHF₃, Ar, O₂ and CO gases are used as theprocess gas.
 13. The plasma treatment method according to claim 1 ,further comprising the steps of, introducing one or more cleaning gasesselected from the group consisting of ClF₃, CF₄ and NF₃ gases into theprocess chamber while keeping a ring and/or a baffle plate attached tothe lower electrode when plasma is stopped; and dry cleaning the ringand/or the baffle plate.
 14. The plasma treatment method according toclaim 1 , further comprising the steps of, detaching the ring and/or thebaffle plate from the lower electrode when plasma is stopped; and drycleaning the ring and/or the baffle plate using at least one or morecleaning gases selected from the group consisting of ClF₃, CF₄ and NF₃.15. The plasma treatment method according to claim 1 , furthercomprising the steps of, detaching the ring and/or the baffle plate fromthe lower electrode when plasma is stopped; and wet cleaning the ringand/or the baffle plate using at least one cleaning solution selectedfrom a group of isopropylalcohol, water and fluorophosphoric acid. 16.The plasma treatment method according to claim 1 , further comprisingthe steps of counting the number of particles adhering to the substratewhich has been treated in the process chamber; and cleaning the ringand/or the baffle plate while keeping plasma stopped when the number ofparticles adhering becomes larger than a predetermined value.
 17. Theplasma treatment method according to claim 1 , further comprising thesteps of, counting the number of particles scattering in atmosphereexhausted from a treatment apparatus and/or at least in one or moreareas in an exhaust pipe; and cleaning the ring and/or the baffle platewhile keeping plasma stopped when the number of particles becomes largerthan a predetermined value.
 18. A plasma treatment apparatus forplasma-treating a substrate, which is to be treated, under decompressedatmosphere comprising: a chamber earthed; means for exhausting thechamber; a lower electrode on which the substrate to be treated ismounted; an upper electrode arranged in the chamber to oppose to thelower electrode; means for supplying process gas to the substrate on thelower electrode through the upper electrode; a first power supplyconnected to the lower electrode through a first matching circuit toapply high frequency power, which has a first frequency f₁ lower than aninherent lower ion transit frequency of the process gas, to the lowerelectrode; a second power supply connected to the upper electrodethrough a second matching circuit to apply high frequency power, whichhas a second frequency f₂ higher than an inherent upper ion transitfrequency of the process gas, to the upper electrode; first filter meansfor removing high frequency components of the second frequency f₂ fromthe high frequency power applied to the lower electrode; and secondfilter means for removing high frequency components of the firstfrequency f₁ from the high frequency power applied to the upperelectrode.
 19. The plasma treatment apparatus according to claim 18 ,wherein the first filter means is connected to a first circuit, whichconnects a first matching circuit to the lower electrode, at an endthereof and the first circuit includes a first earthed capacitor at theother end thereof; and the second filter means is connected to a secondcircuit, which connects the first matching circuit to the upperelectrode, at an end thereof and the second circuit includes, at theother end thereof, a second earthed capacitor and an induction coilconnected in series to the second capacitor.
 20. The plasma treatmentapparatus according to claim 18 , wherein said first filter means has animpedance larger than several kΩ relative to the high frequency powerhaving the first frequency f₁ and an impedance smaller than several Ωrelative to the high frequency power having the second frequency f₂; andsaid second filter means has an impedance smaller than several Ωrelative to the high frequency power having the first frequency f₁ andan impedance larger than several kΩ relative to the high frequency powerhaving the second frequency f₂.
 21. A plasma treatment apparatus forplasma-treating a substrate, which is to be treated, under decompressedatmosphere comprising: a chamber earthed; exhaust means for exhaustingthe chamber; a lower electrode on which the substrate is mounted; anupper electrode arranged in the chamber to oppose to the lowerelectrode; means for supplying process gas to the substrate on the lowerelectrode through the upper electrode; a first power supply connected tothe lower electrode through a first matching circuit to apply highfrequency power, which has a first frequency f₁ lower than an inherentlower ion transit frequency of the process gas, to the lower electrode;a second power supply connected to the upper electrode through a secondmatching circuit to apply high frequency power, which has a secondfrequency f₂ is higher than an inherent upper ion transit frequency ofthe process gas, to the upper electrode; and an amplitude modulatorcircuit connected to the first and second power supplies to modulate theamplitude of the high frequency power having the first frequency f₁ toapply amplitude-modulated high frequency to the upper electrode.
 22. Theplasma treatment apparatus according to claim 18 , wherein said exhaustmeans exhausts the chamber to an internal pressure of 10-250 mtorr. 23.The plasma treatment apparatus according to claim 18 , furthercomprising a ring freely detachably attached to the outer circumferenceof the lower electrode to cause reaction products created by heat orplasma to adhere not to the lower electrode but to the ring.
 24. Theplasma treatment apparatus according to claim 18 , further comprisingthe ring freely detachably attached to the outer circumference of thelower electrode to cause reaction products created by heat or plasma toadhere not to the lower electrode but to the ring; and lifter means formoving the lower electrode up and down together with the ring.
 25. Theplasma treatment apparatus according to claim 18 , wherein the chamberhas an opening through which the substrate to be treated is carried inand out, and the ring is moved up and down between the upper end and thelower and of said opening by the lifter means.
 26. The plasma treatmentapparatus according to claim 25 , further comprising a baffle plateattached to the outer circumference of the ring and positioned higherthan the upper end of said chamber opening, when the ring is lifted, toshield the chamber opening from plasma atmosphere.
 27. The plasmatreatment apparatus according to claim 26 , further comprising anexhaust opening formed in that portion of the chamber aide wall which islower than the top of the lower electrode; and holes formed in thebaffle plate to adjust or rectify the flow of the process gas, whereineach hole in the baffle plate is tilted relative to the vertical axis tocause the process gas, which has passed through the holes, to flow in adirection reverse to the direction in which gas is exhausted by a rotarypump.
 28. The plasma treatment apparatus according to claim 26 , whereinthe baffle member comprises plural plates in which holes each having asubstantially same pitch are formed, and they are placed one upon theothers to shift their corresponding holes a little to form a step-likehole.
 29. The plasma treatment apparatus according to claim 18 , furthercomprising a cover member freely detachably attached to the upperelectrode to cover a peripheral portion thereof so as to preventreaction products from adhering to the upper electrode.
 30. The plasmatreatment apparatus according to claim 29 , wherein the upper electrodehas first engaged recesses or projections formed in or on the outercircumference thereof, the cover member has second engaging projectionsor recesses formed on or in an inner circumference thereof and the covermember is made of elastic material, and the second engaging projectionsor recesses are engaged with the first engaged recesses or projectionswhile elastically deforming the cover member.
 31. The plasma treatmentapparatus according to claim 29 , wherein said cover member includes awall member to cover an upper inner wall of the chamber.
 32. The plasmatreatment apparatus according to claim 18 , wherein an insulating layer,3 mm or more thick, is formed at least on the inner side wall of thechamber.
 33. The plasma treatment apparatus according to claim 18 ,further comprising a vaporizer for vaporizing liquid material from whichthe process gas is created, wherein said vaporizer includes a housingprovided with a liquid material inlet communicated with a liquidmaterial supply supply and with a process gas outlet communicated withthe chamber, and a porous conductive heating unit arranged in thehousing.
 34. The plasma treatment apparatus according to claim 33 ,wherein said vaporizer includes vibrators to vibrate the porousconductive heating unit.
 35. The plasma treatment apparatus according toclaim 33 , wherein said vaporizer in arranged adjacent to a process gasintroducing section of the chamber.
 36. The plasma treatment apparatusaccording to claim 33 , wherein said vaporizer is made integral to theprocess gas introducing section of the chamber.
 37. The plasma treatmentapparatus according to claim 33 , further comprising a bypass arrangedbetween the vaporizer and the process gas introducing section whereinthe process gas outlet of the vaporizer is selectively communicated withone of the bypass and the process gas introducing section.
 38. Theplasma treatment apparatus according to claim 33 , wherein said porousconductive heating unit is a sintered ceramics.
 39. The plasma treatmentapparatus according to claim 33 , wherein a passage through which liquidmaterial flows is formed in the porous conductive heating unit.
 40. Theplasma treatment apparatus according to claim 33 , wherein a second gasintroducing opening is formed downstream the vaporizer and a gas mixingpassage through which plural gases are mixed extends downstream thesecond gas introducing opening.